Apparatus and method for anchoring sutures

ABSTRACT

A suture anchor having a conical surface and a bore in which an end of an insertion tool is inserted. The insertion end of the insertion tool is made of material having elastic properties. The bore and base of the suture anchor are angled with respect to the central axis of the suture anchor and preferably are parallel to each other. During insertion, the suture anchor is reoriented to fit into the hole, thereby bending the elastic end of the insertion tool. When the suture anchor is within cancellous bone tissue, the elastic properties of the insertion tool deploys the suture anchor to an orientation in which the suture anchor cannot fit through the bone hole, thereby firmly anchoring the suture anchor in the human bone.

This is a continuation of U.S. patent application Ser. No. 09/265,022,filed Mar. 9, 1999 now U.S. Pat. No. 6,146,408, by Edwin C. Bartlett forAPPARATUS AND METHOD FOR ANCHORING SUTURES, which is a continuation ofU.S. patent application Ser. No. 08/851,583, filed May 5, 1997 now U.S.Pat. No. 5,879,372, by Edwin C. Bartlett for APPARATUS AND METHOD FORANCHORING SUTURES, which is a continuation of U.S. patent applicationSer. No. 08/308,286, filed Sep. 19, 1994 now U.S. Pat. No. 5,626,612 byEdwin C. Bartlett for APPARATUS AND METHOD FOR ANCHORING SUTURES, whichis a continuation-in-part of 08/124,163 filed Sep. 20, 1993, now U S.Pat. No. 5,540,718; issued Jul. 30, 1996 to Edwin C. Bartlett.

BACKGROUND OF THE INVENTION

This invention relates to an apparatus and method for anchoring suturesto a live human bone. More particularly, this invention relates to asuture anchor made of a substantially rigid, preferably biocompatiblematerial, and most preferably a material that can be incorporated intothe bone as a bone graft, such as bone, and an insertion tool having aportion made of a material having elastic properties which is insertedinto the anchor and functions to orient the suture anchor, once insertedin the bone, to securely anchor the suture.

Suture anchors for anchoring a suture to bone so that another bodytissue, such as muscle or ligament, may be sutured to the bone are knownin the art. Such suture anchors come in a variety of shapes and designs.A survey of such suture anchors may be found in James E. Carpenter etal., “Pull-Out Strength of Five Suture Anchors”, Arthroscopy, 9(1), pp.109-113 (1993).

For example, harpoon-type or screw-type suture anchors are drilled intocortical bone. Examples of such suture anchors are shown, for example,in Cerrier et al. U.S. Pat. No. 5,100,417 and Hayhurst et al. CanadaPat. No. 2,045,903. Such suture anchors are held in place in any of avariety of manners, such as through self-tapping, by a force fit, or byincluding a resilient portion which flexes to frictionally engage thebone material.

Another type of suture anchor includes a rigid member and a resilient,shape memory member. The resilient member is substantially flush withthe rigid member during insertion, and flexes away from the rigid memberonce lodged inside the bone. Such anchors have been described inGatturna et al. U.S. Pat. Nos. 5,046,513 and 5,192,303. The shape memorymaterial may be made in accordance with, for example, Quin U.S. Pat. No.4,505,767 or Harrison U.S. Pat. No. 4,565,589. Because two differentmaterials are used, this type of suture anchor can be costly anddifficult to manufacture. Moreover, the joining of two dissimilar metalsleads to potential flaws and potential breakage at the joint or weldpoint.

A third type of suture anchor is substantially elongated and is insertedwith its longitudinal axis substantially parallel to the bone holethrough which it is inserted. The suture anchor is then reoriented uponreaching cancellous bone tissue by pulling on the suture attached at aselected point along the suture anchor. Examples of such suture anchorsare shown in Hayhurst et al. U.S. Pat. No. 5,041,129 (“Hayhurst”) andNoblitt et al. U.S. Pat. No. 5,203,787 (“Noblitt”). The Hayhurst sutureanchor has a substantially cylindrical rigid body with a central boreand a longitudinal slot extending from one end to approximately themiddle of the rigid body. A suture is positioned inside the centralbore, and the anchor is inserted with the slot entering the bone last.Once the anchor is properly positioned, the suture is pulled through theslot towards the base of the slot, thereby reorienting the suture anchorto fix the anchor in the bone. The Noblitt suture anchor has an offsetportion at which a suture is attached. Once the suture anchor is withincancellous tissue, the suture is pulled, thereby reorienting the sutureanchor so that its longitudinal axis is substantially transverse to thebone hole through which it was inserted. One disadvantage associatedwith this type of anchor is that tugging on the suture to reorient theanchor may put undue stress on the suture (particularly at the base ofthe slot in Hayhurst). Moreover, the only means provided by Hayhurst andNoblitt for reorienting or deploying the suture anchor is by pulling onthe suture that extends from the bone hole after insertion of the sutureanchor. Furthermore, the introduction technique is unduly complicated,requiring several types of insertion tools. It is believed thatinserting and seating the Noblitt suture anchor may present additionaltechnical difficulties because of the portion of the suture anchor whichis offset from the central portion of the elongated body.

A disadvantage common to all of the above-described suture anchors isthat many are typically formed of metal which may not be biocompatible.Additionally, such suture anchors are typically visible during X-ray,magnetic resonance imaging (MRI), and computerized tomography (CT)examinations. Accordingly, these suture anchors may interfere withnoninvasive examinations of the treated area. Moreover, theabove-described suture anchors typically require complex insertiontools, the use of which is time consuming. There is thus greaterpotential for later complications such as bone weakening.

Two other anchoring means are staples and cement. The former isgenerally not desirable because staples can crack the bone in which theyare inserted or damage the tissue to be connected to the bone. Thelatter is generally not desirable because of substance compatibility,the need for particular surface characteristics for adequate bonding,and excessive setting times.

It therefore would be desirable to provide an apparatus for anchoring asuture to a bone which is simple to manufacture and to insert, whichdoes not interfere with noninvasive examinations such as radiographs,MRI, or CT, and which is biocompatible and most preferably, capable ofbeing incorporated into the bone as a bone graft, to strengthen thebone. Additionally, the apparatus may be bioabsorbable.

It would also be desirable to provide a method and apparatus forinserting and deploying a suture anchor which results in a minimalnumber of insertion steps and requires a minimal number of tools.

SUMMARY OF THE INVENTION

It is an object of this invention to provide a suture anchor which issimple and inexpensive to manufacture and easy to insert, as well as amethod of inserting and deploying the suture anchor which is relativelystraightforward having a minimal number of steps, requiring a minimalnumber of insertion tools. Such a system for anchoring a suture to bonereduces later complications such as bone weakening.

It is also an object of this invention to provide a suture anchor whichdoes not interfere with noninvasive examinations such as by radiographs,MRI, or CT, and is biocompatible, thus potentially causing bonestrengthening after implantation. Additionally, the suture anchor may beformed from a bioabsorbable material.

These and other objects of the invention are accomplished in accordancewith the principles of this invention by providing a substantially rigidsuture anchor, preferably made of bone, which is reoriented afterinsertion to be securely positioned inside a bone. A single insertiontool pushes the suture anchor through a previously drilled hole in thebone. The insertion tool includes at least a portion made of shapememory material which is deformed during insertion of the suture anchorbut which returns to its initial configuration or shape when the sutureanchor is able to rotate (e.g., when in cancellous bone tissue), therebyreorienting and deploying the suture anchor to be securely positioned inthe bone.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects and advantages of the invention, its nature,and various features will be more apparent from the following detaileddescription of the preferred embodiments, taken in conjunction with theaccompanying drawings (in which like reference characters represent likeelements throughout), and in which:

FIG. 1 is a side view of a suture anchor having a conical surface inaccordance with the principles of this invention;

FIG. 2 is a side view of a modified suture anchor similar to the sutureanchor of FIG. 1, but with truncated apex in accordance with theprinciples of this invention;

FIG. 3 is a side view of a suture anchor similar to the suture anchor ofFIG. 2, but with rounded edges, in accordance with the principles ofthis invention;

FIG. 4 is another side view of the suture anchor of FIG. 3 rotated 90degree about its central axis;

FIG. 5 is a side view of a suture anchor similar to the suture anchorsof FIGS. 2-4, but having both a conical surface and a cylindricalsurface in accordance with the principles of this invention;

FIG. 6 is another side view of the suture anchor of FIG. 5 rotated 90degree about its central axis;

FIG. 7 is a side view of a suture anchor similar to the suture anchorsof FIGS. 2-6, but having two conical surfaces with their apexes pointedaway from each other in accordance with the principles of thisinvention;

FIG. 8 is another side view of the suture anchor of FIG. 7 rotated 90degrees about its central axis;

FIG. 9 is a side view of an insertion tool in accordance with theprinciples of this invention;

FIG. 10 is a side view of an alternative embodiment of an insertion toolin accordance with the principles of this invention;

FIG. 11 is a side view of another alternative embodiment of an insertiontool in accordance with the principles of this invention;

FIG. 12 is a side view of a modified version of the insertion tool ofFIG. 11 in accordance with the principles of this invention;

FIG. 13 is a side view of a suture threaded through the suture anchor ofthe present invention;

FIG. 14 is a side view of an alternative manner of threading a suturethrough the suture anchor of the present invention;

FIG. 15 is a side view of another alternative manner of threading asuture through the suture anchor of the present invention;

FIG. 16 is a side view of a suture anchor mounted on an insertion tooland carrying a suture, in preparation for insertion into a bone;

FIG. 17 is a side view of a suture anchor mounted on an insertion tooland in the initial stages of insertion into a bone;

FIG. 18 is a side view of a suture anchor mounted on an insertion tool,shown once insertion into a bone has begun;

FIG. 19 is a view similar to that of FIG. 18, but shows further progressof the suture anchor and insertion tool into the bone, in the positionat which the insertion tool is in its most deformed state;

FIG. 20 is a view similar to that of FIG. 19, but shows the insertiontool beginning to resume its initial configuration;

FIG. 21 is a view similar to that of FIG. 20, but shows the sutureanchor almost completely inside the bone, but not yet within a secureanchoring position;

FIG. 22 is a side view of a suture anchor completely positioned incancellous bone tissue, the suture anchor still mounted on the insertiontool, which has resumed its initial configuration;

FIG. 23 is a side view of a suture anchor in a secure anchoringposition, dismounted from the insertion tool;

FIG. 24 is a side view of an alternative form of suture anchor and itsassociated insertion tool;

FIG. 25 is an enlarged side view of the suture anchor shown in FIG. 24;

FIG. 26 is a front view of the suture anchor shown in FIG. 25;

FIG. 27 is a sectional view taken along line 27—27 of FIG. 26;

FIG. 28 is an end view of the suture anchor of FIG. 25; and

FIG. 29 is a perspective view of the suture anchor of FIG. 25.

DETAILED DESCRIPTION OF THE INVENTION

Suture anchors constructed in accordance with the principles of thepresent invention are shown in FIGS. 1-8. Suture anchors 20, 22, 322,522, and 722, which represent preferred embodiments of the presentinvention, are formed from a material which is biocompatible.Preferably, the selected material strengthens the bone in which theanchor is inserted. Additionally, it is desirable for the selectedmaterial to be transparent or translucent to noninvasive examinationssuch as by radiograph (e.g., X-ray). Accordingly, the most preferredmaterial for the suture anchor of the present invention is corticalbone. The suture anchor of the present invention is preferably formedfrom strips of cortical bone cut from the midshaft of a human femur.Autologous bone can be used, but can be difficult to obtain. Allogeneiccortical bone is the preferred material, however, the use of xenogeneiccortical bone tissue is also contemplated. The suture anchor of thepresent invention may also be formed of a suitable biocompatible metal,polymer, or other suitable material, such as polyethylene,polymethylmethacrylate, polysulfone, and similar polymers, preferablypolysulfone. Such metals, polymers, and other materials shouldpreferably be recognized by the appropriate regulatory authority asbeing suitable for use in humans. Additionally, one of a variety ofknown bioabsorbable materials, such as polylactic acid, polydioxanone(Ethicon PDS, Ethicon Inc., Somerville, N.J.), polyglycolic acid andsimilar materials, or blends thereof, may be used. It will beappreciated that the biocompatible material may include suitablebioactive materials, such as hydroxyapatite or tricalcium phosphate, orsuitable bioinert materials, such as alumina or zirconia.

Although the suture anchor of the present invention may be of anydesirable elongated shape, such as a cylinder, the suture anchor of thepresent invention preferably has at least one generally conical surface.The term “conical surface” is to be understood in its usual sense as allor a portion of the surface generated by a moving line intersecting afixed curve referred to as the directrix and a fixed point referred toas the vertex or apex. Thus, the suture anchor of the present inventionmay be a cone (FIG. 1), a truncated cone (FIGS. 2-4) such as a frustum(FIG. 2), a cone and cylinder combination (FIGS. 5 and 6), or a two conecombination (FIGS. 7 and 8). The “central axis” is the line between theapex of the cone and the center of the fixed curve that forms thedirectrix of the cone. In a right cone, the directrix makes a 90 degreeangle with the plane of the directrix. One of the simplest embodimentsof the invention would be a cone in which the base of the suture anchorand the directrix were the same. In the preferred embodiment shown inFIG. 1, the base of the suture anchor is cut oblique to the directrix.

The conical surfaces of the suture anchors shown in FIGS. 1-8 are allderived from right circular conical surfaces. However, the presentinvention also contemplates suture anchors that have a general conicalsurface that deviates from that of a right circular conical surfacewhether in the angle formed by the central axis and the directrix, suchas an oblique conical surface, or in the shape of the directrix, such asan elliptical conical surface or a rhomboid conical surface. In suchembodiments, it would be obvious to one of skill in the art to apply theprinciples set forth herein to produce a suture anchor that wouldfunction in accordance with the method of the present invention.

The length and diameter of the suture anchor are selected to provide thestrongest suture anchor which can fit through the patient bone hole inwhich the suture anchor is to be positioned, and which can accommodatethe suture required for the particular operation.

The apex angle is commonly determined first. The apex angle of sutureanchors 20 and 22 is preferably approximately 20 degrees. Thus, forsuture anchors 20 and 22, central axis 25 forms an approximately 10degree angle with the conical surface 40. This is shown for sutureanchors 20 and 22 in FIGS. 1 and 2, respectively. The apex angle A ofsuture anchors 322, 522 and 722 is preferably approximately 15 degrees.Thus, for suture anchors 322, 522 and 722, central axis 25 preferablyforms an approximately 7.5 degree angle with conical surfaces 340, 540and 740, respectively. This is shown for suture anchors 322, 522 and 722in FIGS. 3, 5 and 7, respectively.

The length of the suture anchors 20, 22, 322, and 722 is preferablyapproximately 0.455 in. (1.156 cm). The length of suture anchor 522 ispreferably approximately 0.440 in. (1.118 cm).

The thickest diameter of suture anchors 20, 22, 322, and 722 ispreferably approximately 0.117 in. (0.297 cm). The diameter of thecylindrical portion of suture anchor 522 is preferably approximately0.113 in. (0.287 cm). The size of the patient bone hole through whichthe suture anchor is inserted is within the range of 1-12 mm, typicallywithin 2-6 mm.

Preferably, the patient bone hole is within 2.5-3.5 mm. The patient bonehole is formed according to any desired method, utilizing any suitablemeans. It should be appreciated that the optimum shape and size of thesuture anchor may vary according to the site of use in the patient. Oneof ordinary skill in the art could determine, by routineexperimentation, the optimum shape and size of the suture anchor for aparticular application at a particular site of use.

Suture anchor 20 of FIG. 1 is a cone with apex 24. Such a suture anchormay be described as having a first conical surface 40, a base 28 closingoff the open end of the conical surface, a central axis 25, and ananchor bore 34 across the conical surface.

A conical suture anchor may easily be formed by inserting an end of astrip of the desired material into a milling, turning or other suitablecutting or shaping device. Such devices are well known in the art. Forexample, a mill may be designed for shaping bone or other materials inaccordance with the principles of a common pencil sharpener.Alternatively, the suture anchor may be formed by casting, molding orany other suitable method.

Apex 24, or a portion thereof, is useful for cutting through cancellousbone tissue once suture anchor 20 passes through the cortical bonetissue. Angle A of apex 24 is selected to efficiently cut throughcancellous bone tissue and can range from 10 degrees-60 degrees.Preferably, apex angle A is between 10 degrees-20 degrees. The exactangle will depend on the apparatus used, and most typically isapproximately 15 degrees-20 degrees.

For greater strength in the apical area, it may be desirable to cut offthe apex of the conical suture anchor to form a flattened trailing end26 (FIG. 2), 326 (FIG. 3), 526 (FIG. 5), 726 (FIG. 7). The angle atwhich the apex is cut may result in a frustoconical suture anchor 22(FIG. 2), or a truncated conical suture anchor 322 (FIGS. 3 and 4), 522(FIGS. 5 and 6), 722 (FIGS. 7 and 8). The amount by which the cone'sapex is truncated should preferably maximize the structural strength ofthe apical region of the suture anchor, while retaining a generalconical shape. This enables travel through cancellous bone tissue duringreorientation and positioning of the suture anchor after insertion.Preferably, the apex is cut so that the trailing end formed is at anapproximately 45 degree angle T with the conical surface to form atruncated conical suture anchor 322, 522, 722 as shown in FIGS. 3, 5,and 7.

Each of suture anchors 20, 22, 322, and 522 has a substantially planarbase 28 which preferably is cut oblique (i.e., neither parallel norperpendicular) to the central axis (the base of suture anchor 722 is asecond conical section). Because base 28 is cut oblique to the centralaxis, the angle formed between the conical surface and the base ofsuture anchors 20, 22, 322, and 522 varies along the circumference ofbase 28. The leading bottom edge 30 (the first area of the edge of base28 to enter the patient bone hole through which the suture anchor is tobe inserted, as further described below) preferably has the smallestangle B between the conical surface and base 28. Accordingly, trailingedge 32, opposite leading edge 30, is at angle C, preferably the largestangle between the conical surface and base 28. Angles B and C are shownin FIGS. 1 and 2.

The specific angle at which base 28 is cut with respect to the centralaxis is determined primarily by the size of the patient bone hole, toachieve the most easily insertable suture anchor. The measurement of theangle formed by the central axis and the conical surface and the desiredlength of the suture anchor also affect the angle at which base 28should be cut. The suture anchor must be sufficiently narrow, in atleast one orientation, such that it is able to fit through the patientbone hole in which the suture anchor is to be positioned. Thus, when thesuture anchor is inserted into the patient bone hole (with base 28parallel to the walls of the patient bone hole) trailing edge 32 shouldbe able to fit into the patient bone hole as well in order to ensurethat the remainder of the suture anchor will be able to fit through thepatient bone hole. Preferably, the widest part of the suture anchor isapproximately 0.2-0.5 mm less than the patient bone hole. Preferably,base 28 is cut at an angle of approximately 45 degrees with respect tothe central axis. Typically, the resulting angle C at the trailing edgeis between 90 degrees-165 degrees, and most preferably approximately 128degrees.

Each of suture anchors 20, 22, 322, 522, and 722 has an anchor bore 34in which an insertion tool is positioned to insert the suture anchorinto the patient bone hole. Preferably, as shown in FIGS. 1, 2, 3, and5, anchor bore 34 is drilled parallel to base 28 extending generally ina direction from the trailing end toward the leading edge. It will beappreciated that bore size may vary according to the overall size of thesuture anchor and the physical requirements of the insertion tool. Forsuture anchors that fit through an approximately 3 mm bone hole, thediameter of anchor bore 34 is preferably between 0.025-0.042 in.(0.635-1.067 mm), most preferably approximately 0.035 in. (0.889 mm).Furthermore, the anchor bore 34 of the suture anchor may be tapered to asmaller diameter as it travels toward the leading edge. Preferably, asshown in FIGS. 3, 5, and 7, the end of anchor bore 34 in which aninsertion tool is inserted has a radiused area 334, 534, 734, having aradius of curvature of approximately 0.1 in. (2.54 mm). The suture maybe threaded through anchor bore 34 alongside the insertion tool.

Alternatively, a separate suture accessory bore 36 (shown in FIGS. 3-8)may be formed substantially perpendicular to anchor bore 34 (FIGS. 4, 6,8) for separately accommodating the suture. As shown in FIGS. 3, 5 and7, preferably accessory bore 36 is located between anchor bore 34 andthe apex of the suture anchor. However, it is within the scope of thepresent invention for the accessory bore to be located between theanchor bore and the base of the suture anchor. The diameter of theaccessory bore 36 may vary according to the size and strength of sutureused. For suture anchors that fit through an approximately 3 mm bonehole, accessory bore 36 preferably has a diameter between 0.019-0.030in. (0.483-0.762 mm), most preferably approximately 0.028 in. (0.7112mm). Bores 34 and 36 will be discussed in greater detail below inconnection with the insertion tool of the present invention and themethod of inserting the suture anchor in accordance with the principlesof the present invention.

The shape of suture anchor 322 of FIGS. 3 and 4 is substantially thesame as suture anchor 22 of FIG. 2, except the edges of suture anchor322 are radiused. Preferably, radiused area 330 of leading edge 30 hasan approximately 0.02 in. (0.508 mm) radius of curvature, and radiusedarea 332 of trailing edge 32 has an approximately 0.12 in. (3.048 mm)radius of curvature. As shown in FIG. 3, base 28 appears mostly rounded.Similarly, suture anchor 522 also has radiused edges. Preferably,radiused area 530 has an approximately 0.02 in. (0.508 mm) radius ofcurvature, and radiused area 532 has an approximately 0.05 in. (1.27 mm)radius of curvature.

In order to reduce stress on the suture anchor at bores 34 and 36,suture anchors 522 and 722 are not conical past the area of bores 34 and36, as shown in FIGS. 5-8.

Suture anchor 522 is formed with a conical surface 540 up to bores 34and 36 and a cylindrical surface 542 extending from bores 34 and 36 tobase 28. Such a suture anchor may be generally described as having afirst conical surface 540, a base 28 closing off the open end of theconical surface, a central axis 25, and an anchor bore 34 across saidconical surface with a cylindrical surface 542 extending between theopen end of the conical surface and the base. The diameter ofcylindrical surface 542 is preferably substantially equal to thediameter of conical surface 540 at transition point 544 from conical tocylindrical. Thus, provided that the suture anchors are of comparablelength and apex angle, the widest part of suture anchor 522 is narrowerthan the widest part of suture anchors 20, 22, and 322 and, accordingly,suture anchor 522 can fit in a narrower patient bone hole. Because ofits strength and size, suture anchor 522 is a particularly preferredembodiment. When measured from end to end, at its largest distance,suture anchor 522 is preferably approximately 0.44 in. (1.1176 cm) inlength.

Instead of having a cylindrical surface after bores 34 and 36, sutureanchor 722 has a secondary conical surface 742, tapering away from bores34 and 36 and primary conical surface 740, as shown in FIGS. 7 and 8.Such a suture may be generally described as having a first conicalsurface 740, a central axis 25, an anchor bore 34 across the conicalsurface and a base comprising a second conical surface 742 inverted withrespect to the first conical surface. Accordingly, the thickest portionof suture anchor 722 is at transition point 744. Preferably, secondaryconical surface 742 has a flattened area 748 adjacent to the insertionend of anchor bore 34 (the end through which the insertion tool isinserted, as described in further detail below) for added suture anchorstrength in the area of the bores.

Suture anchors 20, 22, 322, 522, and 722 have an anchor bore 34 in whichthe insertion tool is positioned to insert the suture anchor, and alsothrough which the suture may be threaded. The diameter of anchor bore 34is determined by the diameter of the insertion tool to be used and, ifthe suture is also threaded through anchor bore 34, the suture to beanchored. Anchor bore 34 may be tapered to provide a tighter fit for theinsertion tool and to increase the strength of the suture anchor(because less material is removed to create the bore). Typically, thediameter of anchor bore 34 is between 1/32- 1/16 inches, and mostpreferably 0.035 in. (0.889 mm).

Anchor bore 34 need not be cylindrical, and may have any of a variety ofcross-sectional shapes. If the suture is to be threaded through anchorbore 34, the shape of anchor bore 34 preferably includes a section inwhich the suture can travel to minimize contact between the suture andthe insertion tool during the insertion process. Potentialcross-sectional shapes for anchor bore 34 thus include oblong,elliptical, tear-drop, a figure eight (thereby providing separate butconnected bores for the suture and the insertion tool), substantiallycircular with a slot for the suture to run through, or any other shapethat can accommodate the suture as described. The entry and exit areasof anchor bore 34 preferably are chamfered or radiused (see radiusedareas 334, 534, 734 in FIGS. 3, 5, and 7, respectively) to reduce stresson the suture when the suture is pulled to reorient the suture anchorand during subsequent suturing. Anchor bore 34 is preferably cut at anangle oblique to the central axis. Preferably, anchor bore 34 and base28 are parallel. However, it is within the scope of the presentinvention to form anchor bore 34 and base 28 at different angles withrespect to the central axis. However, anchor bore 34 should be orientedsuch that, during the process of insertion of the suture anchor, forceapplied by the insertion tool advances leading edge 30 of the sutureanchor toward and through the patient bone hole (as described in furtherdetail below).

In order to minimize contact between the suture and insertion toolduring the insertion process, it is preferable to thread the suturethrough an accessory bore 36 having a diameter of preferablyapproximately 0.028 in. (0.7112 mm). The use of a separate accessorybore 36 for the suture reduces stress that may be put on the suture ifthreaded in anchor bore 34 alongside the insertion tool. Accessory bore36 is preferably substantially perpendicular to anchor bore 34, as seenin the side views of suture anchors 322, 522 and 722 in FIGS. 4, 6, and8, respectively. The location of accessory bore 36 is selected to havethe smallest effect on the strength of the suture anchor because of thedeficit of suture anchor material. One of ordinary skill in the art candetermine, by routine experimentation and an analysis of the geometry ofthe suture anchor, the optimum point at which accessory bore 36 can beplaced without detrimentally effecting the strength of the sutureanchor. The distance of accessory bore 36 from leading edge 30, alongthe axis of the suture anchor, is preferably between 0.15-0.20 in.(3.81-5.08 mm), and most preferably approximately 0.18 in. (4.572 mm) insuture anchors 20, 22, 322, and 722, and 0.16 in. (4.064 mm) in sutureanchor 522.

In order to function properly, the insertion tool should be limited intravel through anchor bore 34 of the suture anchor. Accordingly, theinsertion tool of the present invention has a means for limiting thetravel of its insertion end into anchor bore 34. Examples of insertiontools having means for limiting insertion end travel are shown in FIGS.9-12.

Insertion tool 41 of FIG. 9 has a substantially straight elongated body42 ending with insertion end 44, which is inserted inside anchor bore 34of the suture anchor. Bead 46 demarcates insertion end 44 from theremainder of body 42 and prevents body 42 from entering anchor bore 34.The diameter of insertion end 44 should be sufficiently wide to providea secure fit inside anchor bore 34 of the suture anchor (also accountingfor the amount of suture material, if any, inside anchor bore 34). Thediameter of bead 46 should be substantially larger in diameter thananchor bore 34 in order to limit movement of insertion end 44 throughanchor bore 34.

Insertion tool 48 of FIG. 10 also has a substantially straight elongatedbody 50 ending at insertion end 52. Like insertion tool 41, insertionend 52 of insertion tool 48 is distinctly demarcated from the remainderof body 50 to thereby limit movement of body 50 through anchor bore 34.In this instance, insertion end 52 is narrower than body 50 anddistinctly begins at step 54. Insertion end 52 must be sufficientlythick to form a secure fit within anchor bore 34 of the suture anchorduring insertion into the patient bone hole (also accounting for theamount of suture material, if any, inside anchor bore 34). It will beappreciated that one or both sides of insertion tool 48 may be stepped.

Insertion tool 56 of FIG. 11 has a substantially straight elongated body58, similar to bodies 42 and 50. However, instead of having ademarcation between body 58 and insertion end 60, such as bead 46 orstep 54, insertion tool 56 has a wedged end 62, with the narrowest partat the free end of insertion tool 56. The dimensions of wedge 62 areselected to securely fit within anchor bore 34 of the suture anchor(also accounting for the amount of suture material, if any, insideanchor bore 34) to hold the suture anchor during insertion into thepatient bone. It will be appreciated that one or both sides of insertiontool 56 may be wedged. Insertion tool 56′ of FIG. 12 is substantiallythe same as insertion tool 56, except wedged end 62′ smoothly joins body58, instead of extending away from body 58 into a portion wider thanbody 58, as does wedged end 62. Preferably, wedged end 62′ tapers fromabout 0.062 in. (1.575 mm) down to about 0.016 in. (0.4064 mm).

Insertion tools 41, 48, 56, and 56′ may have a handle (not shown) at theend opposite insertion end 44, 52, 60 to facilitate gripping of theinsertion tool during. insertion of the suture anchor into the patientbone hole. Typically, the hand grip would be wider and longer than body42, 50, and 58.

For reasons as will be described in connection with the method ofinsertion, at least insertion ends 44, 52, and 60 of insertion tools 41,48, 56 and 56′, respectively, should be formed from a material havingelastic properties, preferably superelastic properties, such as a shapememory material. The elastic or superelastic properties of the materialshould be such that the insertion end is not substantially permanentlydeformed during insertion of the suture anchor and will substantiallyreturn the insertion end to an initial configuration (generally theconfiguration of the insertion end at the time it is initially mountedin anchor bore 34, prior to insertion of the suture anchor into thepatient bone). The preferred material for at least the insertion end ofthe insertion tool is a nickel titanium alloy. Such materials areavailable commercially, under the names NITINOL.™. or TINEL.™. (RayChem)or SENTINOL.™. (GAC International, Inc.). Such shape memory alloyshaving superelastic properties are well known in the art. See, e.g.,U.S. Pat. Nos. 4,505,767, and 4,565,589. However, any other shaperetaining material sufficient for properly inserting the suture anchorof the present invention into a patient bone hole may be used. See e.g.,Shirai and Hyashi, Mitsubishi Technical Bulletin, 184, pp. 1-6 (1988).

Any suitable means for attaching the suture to the suture anchor may beused within the scope of the invention. Suture 64 is most preferablythreaded through accessory bore 36 shown in FIGS. 3-8. However, suture64 may instead be threaded through anchor bore 34 of the suture anchorin any preferred manner, such as those illustrated in FIGS. 13-15. Forsake of simplicity, suture anchor 20 is shown in FIGS. 13-15. However,it will be understood that the discussion below relates to attaching asuture to any of the suture anchors of the present invention, includingsuture anchors 322, 522 and 722.

In FIG. 13, one end of suture 64 is threaded through anchor bore 34 andlooped around the conical surface of suture anchor 20 adjacent leadingedge 30. Thus, suture 64 passes through suture anchor 20 only once, asthread through the eye of a needle. When threaded in this manner, suture64 can freely travel through anchor bore 34. When threaded in thismanner, pulling one of the free ends of suture 64 may cause the sutureanchor to rotate approximately 90 degrees.

Suture 64 may, instead, be more fixedly threaded through anchor bore 34,as shown in FIGS. 14 and 15. In FIG. 14, suture 64 is looped over sutureanchor 20, and the free ends of suture 64 are then threaded through theend of anchor bore 34 adjacent leading edge 30, exiting anchor bore 34adjacent trailing edge 32. Suture 64 is then pulled to tighten the looparound suture anchor 20. When an end of suture 64 is pulled, sutureanchor 20 will barely rotate, if at all, maintaining anchor bore 34relatively parallel to the patient bone hole.

Suture 64 is knotted to anchor 20 in FIG. 15. As shown in FIG. 15, onlyone end of suture 64 is threaded through anchor bore 34 as in FIG. 13.However, upon exiting anchor bore 34, knot 66 is formed with the ends ofsuture 64 at the exit of anchor bore 34, preferably adjacent trailingedge 32. As in FIG. 14, the manner of threading shown in FIG. 15 mayproduce minimal rotation of suture anchor 20 if an end of suture 64 ispulled.

The preferred method of inserting the suture anchor of the presentinvention is illustrated in FIGS. 16-23. For the sake of simplicity,suture anchor 20 is shown. It will be understood that any of sutureanchors 22, 322, 522, or 722 may be used in the method described below.A patient bone hole 70 has already been drilled into patient bone 72.Patient bone hole 70 extends completely through cortical bone matter 74.Patient bone hole 70 may also extend, at least partially, throughcancellous bone tissue 76, preferably to a depth about equal to thelength of the suture anchor. It will be understood that any insertiontool with a shape memory insertion end may be used in the preferredinsertion method. Moreover, any suitable substantially rigid anchor witha bore for the insertion tool may be used. This method is illustratedschematically in FIGS. 16-23.

As shown in FIG. 16, suture 64 is threaded through anchor bore 34, andsuture anchor 20 is mounted on insertion end 44 of insertion tool 41.Insertion end 44 enters anchor bore 34 adjacent trailing edge 32 ofsuture anchor 20 and exits (if at all) adjacent leading edge 30. Becauseinsertion end 44 of tool 41 is securely positioned within anchor bore34, anchor bore 34 is not easily distinguishable, in the Figs., from theouter surface of insertion end 44. Anchor bore 34 is preferably drilledparallel to base 28 such that force applied by the insertion tooladvances the leading edge of the suture anchor toward the patient bonehole. Insertion tool 41 is positioned parallel to the longitudinal axisof patient bone hole 70, maintaining anchor bore 34 and base 28 (ifanchor bore 34 is drilled parallel to base 28) parallel to patient bonehole 70, as well. Leading edge 30 of suture anchor 20 is positioned tobe the first portion of suture anchor 20 to enter patient bone hole 70.

Initial entry of suture anchor 20 into patient bone hole 70 is shown inFIG. 17. The conical surface extending between leading edge 30 and apex24 has not yet encountered patient bone hole 70. As alluded to above,this portion of the conical surface of suture anchor 20 should notencounter patient bone hole 70 until trailing edge 32 also encounterspatient bone hole 70.

Once the conical surface extending between leading edge 30 and apex 24encounters patient bone hole 70, suture anchor 20 begins to rotate orreorient, as shown in FIG. 18, in order to fit into patient bone hole70. Main body 42 of insertion tool 41 is maintained parallel to patientbone hole 70. Thus, when suture anchor 20 reorients, insertion end 44bends.

Typically, insertion end 44 is bent to the greatest extent immediatelybefore trailing edge 32 leaves the portion of patient bone hole 70 inpatient cortical bone tissue 74, as shown in FIG. 19. Once trailing edge32 begins traveling through patient cancellous bone tissue 76, insertionend 44 begins to resume its initially straight configuration, as shownin FIGS. 20 and 21, thereby deploying the suture anchor. Preferably mainbody 42 of insertion tool 41 is not as flexible as insertion end 44, andremains straight throughout the insertion procedure.

Once apex 24 has cleared patient cortical bone tissue 74, and the entiresuture anchor is in cancellous bone tissue 76, insertion end 44 ofinsertion tool 41 is able to return to its original configuration, asshown in FIG. 22. The pointed shape of apex 24 allows suture anchor 20to more easily cut through cancellous bone tissue 76 so that the sutureanchor may be reoriented and secured in its final position. As shown inFIG. 23, insertion tool 41 can then be disengaged from the suture anchorand removed. Pulling the suture 64 up and away from patient bone 72 atthis point may aid in dismounting the suture anchor from the insertiontool in addition to rotating and thereby properly seating suture anchor20 in cancellous bone tissue 76. Preferably suture 64 is once againpulled up and away from patient bone 72 after the insertion tool isremoved to firmly position suture anchor 20 in patient bone 72,preferably against the undersurface of cortical bone 74, within thetransition region between cortical bone matter 74 and cancellous bonematter 76. Typically, suture 64 will be substantially centered withinpatient bone hole 70, and suture anchor 20 will be substantiallyhorizontal. Suturing of body tissue to patient bone 72 can now becommenced.

EXAMPLE 1

Suture anchors substantially as shown in FIGS. 5 and 6, made from bonyallograft, were fashioned from 4-8 mm strips of hydrated cortical bone.Initial conical shaping was done on a medium grain stone grinding wheel.The conical shape was then made uniform with a mill made from a pencilsharpener. An anchor bore and an accessory bore were then drilled usinga guide jig to control size and location. Final smoothing and shapingincluding the cylindrical portion of the anchor was done with a dremeltool. The dimensions of the final suture anchor were as set out abovefor the preferred embodiment of suture anchor 522.

An insertion tool substantially as shown in FIG. 12 was shaped from0.062 in. (1.575 mm) NITINOL.™. ground to a tapered tip (using twogrinding wheels on a centerless grinding tool). A handle was fashionedfrom a stainless steel dowel drilled to accept the body of the insertiontool.

Human cadaveric humerus and pig pelvis in which a hole of about 3 mm wasdrilled was used as a model to test pull-out strength of the abovesuture anchor. Steel wire (26 gauge) was threaded through the accessorybore of the suture anchor to assure that anchor failure rather thansuture failure was tested.

The threaded suture anchor was mounted on the insertion tip of theinsertion tool and advanced into the bone hole with the body of theinsertion tool parallel to the longitudinal axis of the bone hole. Oncethe suture anchor was deployed, the insertion device was removed and theends of the stainless steel suture were tied to form a loop. The sutureanchors were tested to anchor failure using a spring loaded scale withan automatic marker. Failure strength greater than 30 lbs. exceedsindustry standards.

Several tests were performed. For each trial, the load at failure andthe type of failure were determined. Anchor failure was defined as thesuture anchor breaking. The ultimate failure strength of a suture anchorwas recorded as the maximal force applied when the anchor broke. Theseresults did not include those trials in which the anchor pulled out ofthe bone.

The measured failure strengths of a suture anchor formed from bonyallograft was consistently measured at greater than 32 pounds. Thismeasured failure strength far exceeds the industry standard.

EXAMPLE 2

Suture anchors substantially as shown in FIGS. 5 and 6, made of thebiocompatible polymer polysulfone, were fashioned by drillingcylindrical stock polysulfone. The suture anchors were then shaped on alathe. The bores were then radiused and the ends cut. The dimensionswere as set out above for the preferred embodiment of suture anchor 522.

An insertion tool fashioned as described in Example 1 was used toimplant the anchors into specimens of human humerus and pig pelvis.Several tests of suture anchor strength were performed as outlined inExample 1.

The measured failure strengths of a suture anchor formed frompolysulfone was consistently measured at greater than 32 pounds. Thismeasured failure strength far exceeds industry standards.

ADDITIONAL CONSTRUCTIONS

In some circumstances it may be desirable to use more than one suture toattach soft tissue to bone. However, with the suture anchors shown inFIGS. 3-8 and 16-23, where the suture 64 is passed through a roundsuture bore 36, the use of multiple sutures requires either that (i) thesize (i.e., the diameter) of the suture 64 must be reduced so that moresuture can be positioned within the bore 36, and/or (ii) the size (i.e.,the diameter) of the suture bore 36 must be enlarged so as toaccommodate more suture.

However, it is generally not desirable to reduce the size of the sutureany more than is necessary, since this reduces suture strength. At thesame time, it is also generally not desirable to enlarge the diameter ofsuture bore 36 any more than is necessary, since this reduces the amountof material remaining in the suture anchor's body and hence reduces thestrength of the suture anchor's body.

Looking next at FIGS. 24-28, there is shown a novel suture anchor 822also formed in accordance with the present invention. Suture anchor 822is generally similar to the suture anchor 522 shown in FIG. 5, in thesense that it is formed with a conical surface 840 up to openings 34Aand 36A, and a cylindrical surface 842 extending from openings 34A and36A to base 28. However, suture anchor 822 is dissimilar to the sutureanchor 522 shown in FIG. 5 in the sense that the round hole 36 in sutureanchor 522 has been replaced by an elongaged slot 36A. Slot 36A ispreferably sized so as to have a width approximately equal to thediameter of a suture 64. Slot 36A is also preferably sized so as to havea length approximately equal to (N×D), where N is the number of suturesto be attached to the suture anchor and D is the diameter of the suture.Thus, in one preferred embodiment where two lengths of suture 64 are tobe attached to suture anchor 822, slot 36A preferably has a length whichis approximately twice the diameter of the suture.

By using a slot 36A rather than a round opening 36, more than one suturecan be attached to suture anchor 822 while still maintaining maximumsuture strength and maximum anchor body strength.

Furthermore, if desired, suture anchor 822 can also have a taperedopening 36A for receiving the tapered distal end of insertion tool 41A.

It will be understood that the foregoing is merely illustrative of theprinciples of this invention, and that various modifications can be madeby those skilled in the art without departing from the scope and spiritof the invention. For example, the suture anchors and insertion toolsused in the preferred insertion method (illustrated in FIGS. 16-23) maybe formed in shapes other than those illustrated, but which willfunction in accordance with the method of the present invention.Moreover, it will be appreciated that although it is not necessary touse the insertion tools typically used during suture anchor insertion(such as cannulas), the use of such tools is contemplated within thescope of the present invention.

Thus, it will be appreciated that the scope of this invention includesall alternative embodiments and variations which are defined in theforegoing specification and by the claims appended hereto; and theinvention is not to be limited by the specific embodiments that havebeen presented herein by way of example.

1. A suture anchor comprising: an elongaged body having a first end anda second end, said first end being larger than said second end, and anouter surface extending between said first end and said second end; acentral axis extending between said first end and said second end; anopening extending through said elongated body from a first location onsaid outer surface to a second location on said outer surface, saidopening being located closer to said first end than said second end; anda slot extending through said elongated body from a third location onsaid outer surface to a fourth location on said outer surface, said slothaving a width substantially the same as a diameter of a suture, and alength at least twice the diameter of the suture, said slot beingadapted to receive at least two lengths of the suture therethrough.
 2. Asuture anchor according to claim 1 wherein said opening extends at anacute angle to said central axis.
 3. A suture anchor according to claim2 wherein said first end extends at an acute angle to said central axis.4. A suture anchor according to claim 3 wherein said first end extendsparallel to said opening.
 5. The suture anchor in accordance with claim1 wherein said slot is provided with a width of about 0.019-0.030 in. 6.The suture anchor in accordance with claim 5 wherein said slot isprovided with a width of about 0.028 in.
 7. The suture anchor inaccordance with claim 1 wherein said slot is removed from said secondend along said central axis a distance of about 0.15-0.20 in.
 8. Thesuture anchor in accordance with claim 7 wherein said slot is removedfrom said second end along said central axis a distance of about0.16-0.18 in.
 9. The suture anchor in accordance with claim 1 whereinsaid slot extends through the anchor substantially perpendicular to saidopening.